Hand-held, multi-channel pipettors are designed to enable laboratory workers to transfer multiple samples or reagents from one series of containers to another series of containers, such as from one row of wells in a microtiter plate to another row of wells in another microtiter plate. While some multi-channel pipettors rely on manually powered piston movement for aspirating and dispensing, many use electronically controlled stepper motors to control piston movement for aspirating and dispensing. It is quite common in laboratories to have microtiter plates or well plates with 24, 96, 384, or 1536 wells in an array of rows and columns. Typically, but not always, the center line spacing between wells is 9 mm or some fraction or multiple thereof. Center-to-center spacing between pipette tip mounting shafts is therefore often fixed in multi-channel pipettors, for example, 9 mm or 4.5 mm spacing.
On the other hand, some multi-channel electronic pipettors allow the user to manually adjust the center-to-center spacing between the tip fittings. This feature allows lab workers to transfer multiple samples of liquids from a series of containers having one center line spacing to another series of containers having different center line spacing. In other words, some hand-held pipettors on the market allow the user to reposition the pipette tips so that a sample or reagent can be aspirated into multiple pipette tips from a series of wells, tube or other containers having a first center-to-center spacing (e.g. 4.5 mm) and then dispensed into another series of wells, tubes or other containers having a different spacing (e.g. 9 mm). For example, U.S. Pat. No. 6,235,244 discloses a multi-channel pipettor where the center line spacing between the tip fittings is controlled manually by a scissors mechanism actuated by pulling a rod on the exterior of the pipettor. The mounting shafts or fittings for the pipette tips are attached to the scissors mechanism which expands or contracts as needed to reposition the pipette tips. The individual fittings slide along a path defined by a slotted track in the housing for the lower multi-channel assembly. In this design, the complexity of the scissors mechanism, as well as its off-center drive point, can produce inaccuracies in the center-to-center spacing for the individual tip fittings. These units also require two hand operation; one hand for holding the unit and the other to operate the change-in-spacing mechanism.
In contrast to hand-held pipettors, automated, stationary pipetting systems have in the past used roller drums with cam tracks to adjust the center-to-center spacing between pipette tip mounting shafts, again in order to facilitate aspiration from a first series of containers or wells and dispensing into a second series having a different center line spacing. Such a system is disclosed in U.S. Pat. No. 4,830,832. Of course, design constraints for stationary lab equipment as to size and scale are not critical, as compared to hand-held pipettors. With hand-held pipettors, it is important that the design be compact, and that weight be kept to a minimum. It is also particularly important that the width of the lower multi-channel assembly from front to back be kept slender in order to allow the user to easily view the mounted pipette tips. Further, it is important to keep the overall height of the pipettor at a minimum in order to optimize ergonomics and control. In addition, it is important that hand-held, electronic pipettors, not only provide accurate pipetting functions as well as accurate tip spacing, but also provide a smooth operating mechanism that draws minimal power, allow one handed operation and employ an intuitive control system.